The invention relates to a high pressure discharge lamp for motor vehicle headlights.
A high-pressure discharge lamp for a motor vehicle headlight is disclosed, for example, in European Laid-open Specification EP-A 0 786 791. The high-pressure discharge lamp described in this document has a discharge vessel in which there are arranged electrodes for generating a light-emitting gas discharge, an outer bulb surrounding the discharge vessel, and a plastic base which is provided with the electric terminals of the high-pressure discharge lamp and in which the lamp vessels are fixed. The base is provided with a flange which serves to mount the high-pressure discharge lamp in a motor vehicle headlight for high-pressure discharge lamps. The mounting position of a headlight lamp is usually defined by mutually coordinated positioning means on the annular flange and on the lamp holder of the motor vehicle headlight This purpose is usually served by three asymmetrically constructed reference noses integrally formed on the annular flange, which extend radially outwards and engage in corresponding cutouts in the lamp holder of the motor vehicle headlight. In addition, the reference noses also serve as coding means for the type of lamp. Thus, in the case of commercially available headlight lamps such as, for example, H4 or H7 halogen incandescent lamps, the annular flange is constructed differently in a corresponding fashion in order to exclude confusion when the lamp is changed.
It is the object of the invention to use the simplest possible means to retrofit high-pressure discharge lamps which are intended for mounting in motor vehicle headlights specifically designed for them, in such a way that they can be mounted in motor vehicle headlights for halogen incandescent lamps.
The high-pressure discharge lamp according to the invention is provided for use in a motor vehicle headlight, and has at least one transparent lamp vessel and means for generating a light-emitting gas discharge as well as a base which is provided with electric terminals and in which the at least one transparent lamp vessel is fixed The base is provided with an annular flange for the purpose of mounting the high-pressure discharge lamp in the holder of a motor vehicle headlight, the annular flange being adapted according to the invention to the holders of motor vehicle headlights for halogen incandescent lamps, and being fastened on the base by means of a snap or latching connection.
High-pressure discharge lamps can be retrofitted in a simple way by means of the above-named measures such that they can also be mounted in motor vehicle headlights for halogen incandescent lamps. For example, the annular flange is coordinated with the holder of the motor vehicle headlight for an H7 lamp or an H4 lamp. In this case, the high-pressure discharge lamp according to the invention can be operated as a motor vehicle headlight lamp instead of an H7 lamp or an H4 lamp in the H7 lamp holder or H4 lamp holder of the motor vehicle headlight. According to the invention, the annular flange is fixed on the base of the high-pressure discharge lamp by means of a snap or latching connection. Surprisingly, it has been proved that the snap or latching connection between the base and the annular flange ensures a reliable fastening of the flange on the base and, moreover, also ensures adjustment of the luminous means in the headlight reflector. There is consequently no need for any complicated changes on the base in order to retrofit the high-pressure discharge lamp. Moreover, the same tools can be used to produce the annular flange as are used to fabricate the corresponding halogen incandescent lamp.
The above named snap or latching connection is advantageously formed by a groove arranged in the base and a plurality of lugs which are arranged on the annular flange and are provided for engaging in the groove. The groove is preferably arranged in the outer wall of the base, and can therefore also still be provided subsequently by milling in the case of already fabricated high-pressure discharge lamps. The lugs arranged on the annular flange have a spring action and therefore ensure in a simple way that the annular flange can be snapped or latched into the groove in the base. The lugs are preferably arranged in an annular manner and extend radially inward, and the free ends of the lugs define the diameter of the annular opening or the inside diameter of the annular flange. In order to be able to establish the mounting position of the high-pressure discharge lamp uniquely, the base and the flange advantageously have means which are coordinated with one another and prevent rotary movements of the annular flange with reference to the base. It is preferred for this purpose to provide one of the lugs of the annular flange with a cutout in which a web arranged in the groove engages.
The base of the high-pressure discharge lamp according to the invention advantageously consists of an electrically insulating material, preferably of a plastic, in order to ensure an adequate high voltage strength The annular flange advantageously consists of a metal, preferably of a stainless steel or of German silver. As a result, the annular flange has a high mechanical stability. Moreover, as already mentioned above, in this case the same tools can be used to manufacture the annular flange as are used to fabricate halogen incandescent lamps.
Metal fastening means anchored in the base are provided for holding and/or adjusting the at least one lamp vessel in the base. In the region of these fastening means, the annular flange advantageously has cutouts which extend the annular opening of the flange, in order to avoid electric flashovers, corona discharges or leakage currents between the fastening means and the annular flange.
In the high-pressure discharge lamp according to the invention, the annular opening of the annular flange is advantageously arranged relative to the positioning means of the annular flange, which determine the mounting position of the high-pressure discharge lamp in the headlight, in such a way that after the mounting of the high-pressure discharge lamp in the motor vehicle headlight the longitudinal axis of the at least one lamp vessel is displaced in a fashion parallel to the optical axis of the headlight reflector. The convection-induced curvature of the light-emitting discharge arc in the case of its optical imaging in the reflector is taken into account by means of this measure.
If the high-pressure discharge lamp according to the invention is used as a substitute for an H4 lamp in an appropriate motor vehicle headlight, the high-pressure discharge lamp according to the invention is advantageously provided with a means for shielding light, in order to generate the light distribution corresponding to the passing beam. The means for shielding light is preferably constructed as a metal sheet partially surrounding the at least one lamp vessel. For reasons of fabrication, the metal sheet is preferably fastened on the annular flange or constructed in one piece with the annular flange. In the latter case, the annular flange and the metal sheet can be produced jointly in a single deep-drawing process.